Patella fractures represent approximately 1% of all fractures and can be debilitating injuries resulting in extensor mechanism weakness, decreased knee range of motion, anterior knee pain, and degenerative patellofemoral arthritis. The limited soft tissue coverage and importance of the patella in knee extensor mechanism function has made operative treatment of these injuries challenging.
Historically, patellar fractures were treated non-operatively, which was thought to allow for adequate pain relief and partial restoration of extensor mechanism function. However, as surgical knowledge and technique has advanced, management of these injuries has evolved from non-operative care or patellectomy to anatomic reduction and internal fixation with a goal of osseous union.
Today, a non-operative treatment course can be recommended for non-displaced fractures of the patella, particularly when the fracture is non-displaced, the articular surface is not disrupted, and the extensor mechanism is intact. However, a disruption of the articular surface of as little as 2 mm or separation of bone fragments by as little as 3 mm is conventionally associated with an unacceptable risk of unsuitable bone healing. Additionally, patients with patella fractures often have concurrent retinacular tears that can result in fracture displacement and disruption of the extensor mechanism. Further, because of the important role of the patella in maintaining normal kinematics of the knee, operative management is considered to be the treatment of choice for patella fractures when patellar bone fragments are displaced, or the articular surface is disrupted.
One construct commonly used for the operative fixation of patella fractures is a tension band. In particular, an anterior tension band is applied by passing wires or braided cables or sutures behind previously implanted K-wires at the superior and inferior poles, crossing them, and twisting the ends to create a figure-eight pattern. Further, a wire or braided cable can be wrapped circumferentially around the patella directly on bone at a location anterior to the previously placed wires, and is tightened by twisting. A modification of this technique can be performed by replacing the K-wires with cannulated screws, such that a wire or braided cable or suture can be passed through the cannulated screws to create the anterior tension band with a figure-eight configuration, followed by application of a cerclage wire directly on the circumference of the patella.
While tension band constructs are the most common method of fixation, anterior knee pain, failure of the construct, and functional limitation with tension band fixation have all been reported. Further, this technique often fails to address inferior pole comminution commonly seen in fractures of the patella.
More recently, biomechanical studies have shown an advantage to fixation of patella fractures with plating constructs as opposed to tension band fixation. While various different patella plating constructs in use today can achieve satisfactory fracture reductions, the ultimate outcomes are often ineffective and clinically poor. In particular, despite reliable fracture healing and restoration of the extensor mechanisms, outcomes often remain unacceptable with convention techniques. A common misconception among surgeons is that patients recovering from patella fracture fixation mostly do well. However, this is likely because patients are not followed long enough post-operatively. Anterior knee pain after patellar fracture fixation is a common complaint during daily activity. Potential causes include patella baja, extensor mechanism malalignment, articular injury and posttraumatic arthritis, painful implants, or avascular necrosis. This anterior knee pain leads to limited rehabilitation and functional impairment.
Still another surgical option is to perform a partial or total patellectomy, though these procedures are typically reserved for extreme cases such as open injuries. Patellectomy procedures produce a high risk for creating patella baja, and bone-to-bone healing is preferred over tendon-to-bone healing. Also, a partial patellectomy procedure is likely to disrupt the main blood supply to the patella as it enters the inferior pole.
In other instances of an isolated inferior pole fracture that does not include the articular surface, fracture repairs are sometimes performed with what are commonly known as Krackow sutures. In particular, Krackow sutures are placed on the medial and lateral aspects of the patellar tendon, and retrograde drill holes are created from the interior pole to the superior apex of the patella. The sutures are then passed through the drill holes and tied over the superior bony edge of the patella.